We will attempt to improve and further develop immunoassay procedures to measure parathyroid peptides and calcitonin in biological fluids. These methods be applied to studies of mineral methabolism in normally growing children and in children with a variety of disease states. Included will be studies during pregnancy and the prenatal period with emphasis on elucidating the factors involved in the pathogenesis of neonatal hypocalcemia. We will continue and extend studies that relate to the interrelationship between magnesium and parathyroid function and we will further investigate the interrelationship between magnesium and calcitonin. In vivo and in vitro experimental animal studies will complement clinical inve tigations. Laboratory methods in these studies will include immunoassay determinations of serum parathyroid peptides, calcitonin and glucagon, measurements of urinary cyclic AMP and hydroxyproline and determinations of serum 25 hydroxycholecalciferol and ionized calcium activity and of serum and urinary calcium, magnesium and phosphorus.